Theoretical Physics made a huge leap from concept to reality yesterday thanks to collaboration between an international team of scientists and researchers with the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab).

The team has proposed the experimental design of a space-time crystal that is based on an electric-field ion trap and the Coulomb repulsion of particles that carry the same electrical charge. “The electric field of the ion trap holds charged particles in place and Coulomb repulsion causes them to spontaneously form a spatial ring crystal,” says Xiang Zhang, a faculty scientist with Berkeley Lab’s Materials Sciences Division who led this research. “Under the application of a weak static magnetic field, this ring-shaped ion crystal will begin a rotation that will never stop.

The persistent rotation of trapped ions produces temporal order, leading to the formation of a space-time crystal at the lowest quantum energy state.” Professor Zhang, the Ernest S. Kuh Endowed Chair Professor of Mechanical Engineering at the University of California, Berkeley (UC), is also the director of Harvard’s Nanoscale Science and Engineering Center. He authored the paper describing this work in the Physical Review Letters. The paper, entitled “Space-time crystals of trapped ions” was also co-authored by Tongcang Li, Zhe-Xuan Gong, Zhang-Qi Yin, Haitao Quan, Xiaobo Yin, Peng Zhang and Luming Duan.

To understand Zhang’s contribution, it is important to review what was known about crystals in the physical world up until yesterday. Traditional crystals are solid, three-dimensional structures made up of atoms or molecules that bond together in an orderly and repeating pattern. A few common examples of crystals include ice, salt and snowflakes. Crystallization only takes place when heat is removed from a molecular system and it is allowed to reach a lower energy state. At a certain point, continuous spatial symmetry breaks down the crystal and assumes what is known as “discrete symmetry”, which means that instead of the structure being the same in all directions, it is the same in only a few directions.

As mind-boggling as the concept may be for most of us, these researchers were able to harness the properties of crystal formation to devise a clock that operates in 4 dimensions, needs no power source and will keep time even after the universe as we know it comes to an end.“While a space-time crystal looks like a perpetual motion machine and may seem implausible at first glance, keep in mind that a superconductor or even a normal metal ring can support persistent electron currents in its quantum ground state under the right conditions,” explained Tongcang Li, lead author of the study and a post-doc in Zhang’s research group.